NAME
gpgwrap - a small wrapper for gpg
SYNOPSIS
gpgwrap -V
gpgwrap -P [-v] [-i] [-a] [-p <file>]
gpgwrap -F [-v] [-i] [-a] [-c] [-p <file>] [-o <name>] [--] <file>
[<file> ... ]
gpgwrap [-v] [-i] [-a] [-p <file>] [-o <name>] [--] gpg [gpg options]
DESCRIPTION
The GNU Privacy Guard (gpg) supplies the option --passphrase-fd. This
instructs gpg to read the passphrase from the given file descriptor.
Usually this file descriptor is opened before gpg is executed via
execvp(3). Exactly that is what gpgwrap is doing. The passphrase may be
passed to gpgwrap in 4 ways:
* as file path, whereat the passphrase is stored as plain text
in the file
* it is piped from another program to the stdin of gpgwrap
* through the GPGWRAP_PASSPHRASE environment variable
* gpgwrap prompts for it
With no precautions the first point undermines the secure
infrastructure gpg provides. But in pure batch oriented environments
this may be what you want. Otherwise if you are willing to enter
passphrases once and don’t want them to be stored as plain text in a
file gpg-agent is what you are looking for. Another security objection
could be the use of the environment variable GPGWRAP_PASSPHRASE which
contains the passphrase and may be read by other processes of the same
user.
OPTIONS
-V, --version
Print out version and exit.
-P, --print
Get the passphrase and print it mangled to stdout.
-F, --file
Read gpg commands from the given files. If <file> is - it is
read from stdin. Exactly one command per line is expected. The
given line is handled in the following way:
* In the first place the passphrase is mangled. This means that
unusual characters are replaced by their backslash escaped
octal numbers.
* Secondly the mangled passphrase is stored in the environment
variable GPGWRAP_PASSPHRASE.
* "exec gpgwrap -- " is prepended to each line, before the
result is passed as argument to "sh -c".
-h, --help
Print out usage information.
-v, --verbose
Increase verbosity level.
-i, --interactive
Always prompt for passphrase (ignores -p and the environment
variable).
-a, --ask-twice
Ask twice if prompting for a passphrase.
-c, --check-exit-code
While reading gpg commands from a file, gpgwrap ignores per
default the exit code of its child processes. This option
enables the check of the exit code. If a child terminates
abnormal or with an exit code not equal 0 gpgwrap stops
immediately and does return with this exit code. See also
section BUGS.
-p <file>, --passphrase-file <file>
Read passphrase from <file>. If <file> is - it is read from
stdin. The passphrase is expected to be in plain text. If this
option is not given the passphrase will be taken either from
the environment variable GPGWRAP_PASSPHRASE or it will be
prompted on the controlling tty if the environment variable is
not set.
-o <name>, --option-name <name>
Specify the name of the "--passphrase-fd" option understood by
the program to be executed. This is useful if you want to use
gpgwrap in combination with other programs than gpg.
LIMITATIONS
The given passphrase is subject to several limitations depending on the
way it was passed to gpgwrap:
* There is a size limitation: the passphrase should be not
larger than some kilobytes (examine the source code for the
exact limit).
* gpgwrap allows you to use all characters in a passphrase even
\000, but this does not mean that gpg will accept it. gpg may
reject your passphrase or may only read a part of it, if it
contains characters like \012 (in C also known as \n).
* If you set the environment variable GPGWRAP_PASSPHRASE you
should take special care with the backslash character, because
gpgwrap uses backslash to escape octal numbers, (see option
-F). Therefore write backslash itself as octal number: \134.
EXAMPLES
1.
gpgwrap -p /path/to/a/secret/file \
gpg -c -z 0 --batch --no-tty \
--cipher-algo blowfish < infile > outfile
Read passphrase from /path/to/a/secret/file and execute gpg to
do symmetric encryption of infile and write it to outfile.
2.
gpgwrap -i -a \
gpg -c -z 0 --batch --no-tty \
--cipher-algo blowfish < infile > outfile
Same as above except that gpgwrap prompts twice for the
passphrase.
3.
gpgwrap -F -i - <<EOL
gpg --decrypt --batch --no-tty < "$HOME/infile1" > "$HOME/outfile1"
gpg --decrypt --batch --no-tty < "$HOME/infile2" > "$HOME/outfile2"
gpg --decrypt --batch --no-tty < "$HOME/infile3" > "$HOME/outfile3"
gpg --decrypt --batch --no-tty < "$HOME/infile4" > "$HOME/outfile4"
EOL
gpgwrap prompts for the passphrase and executes four instances
of gpg to decrypt the given files.
4.
GPGWRAP_PASSPHRASE="mysecretpassphrase"
export GPGWRAP_PASSPHRASE
gpgwrap -F -c -v /tmp/cmdfile1 - /tmp/cmdfile2 <<EOL
gpg --decrypt --batch --no-tty < "$HOME/infile1" > "$HOME/outfile1"
gpg --decrypt --batch --no-tty < "$HOME/infile2" > "$HOME/outfile2"
gpg --decrypt --batch --no-tty < "$HOME/infile3" > "$HOME/outfile3"
gpg --decrypt --batch --no-tty < "$HOME/infile4" > "$HOME/outfile4"
EOL
Same as above except that gpgwrap gets the passphrase via the
environment variable, reads commands additionally from other
files and checks the exit code of every gpg instance. This
means if one gpg command has a non zero exit code, no further
commands are executed. Furthermore gpgwrap produces verbose
output.
5.
GPGWRAP_PASSPHRASE="$(gpgwrap -P -i -a)"
export GPGWRAP_PASSPHRASE
find . -maxdepth 1 -type f |
while read FILE; do
FILE2="$FILE.bz2.gpg"
bzip2 -c "$FILE" |
gpgwrap gpg -c -z 0 --batch --no-tty \
--cipher-algo blowfish > "$FILE2" &&
touch -r "$FILE" "$FILE2" &&
rm -f "$FILE"
done
Read in passphrase, compress all files in the current
directory, encrypt them and keep date from original file.
6.
find . -maxdepth 1 -type f -name ’*.bz2.gpg’ |
awk ’{
printf("gpg --decrypt --batch --no-tty --quiet ");
printf("--no-secmem-warning < %s\n", $0);
}’ |
gpgwrap -F -i -c - |
bzip2 -d -c - |
grep -i ’data’
Decrypt all *.bz2.gpg files in the current directory,
decompress them and print out all occurances of data. If you
pipe the result to less you get into trouble because gpgwrap
and less try to read from the TTY at the same time. In such a
case it is better to use the environment variable to give the
passphrase (the example above shows how to do this).
7.
GPGWRAP_PASSPHRASE="$(gpgwrap -P -i -a)"
export GPGWRAP_PASSPHRASE
gpgwrap -P |
ssh -C -x -P -l user host "
GPGWRAP_PASSPHRASE=\"\$(cat)\"
...
"
Prompt for a passphrase twice and write it to the
GPGWRAP_PASSPHRASE environment variable.
8.
echo -n "Passphrase: "
stty -echo
read GPGWRAP_PASSPHRASE
echo
stty echo
export GPGWRAP_PASSPHRASE
Another way to prompt manually for the passphrase. It was
needed in combination with older versions of gpgwrap, because
they did not upport -P. Be aware that with this method no
automatic conversion to backslash escaped octal numbers takes
place.
9.
echo "mysecretpassphrase" |
gpg --batch --no-tty --passphrase-fd 0 \
--output outfile --decrypt infile
Cheap method to give passphrase to gpg without gpgwrap. Note
that you can’t use stdin to pass a file to gpg, because stdin
is already used for the passphrase.
10.
gpg --batch --no-tty \
--passphrase-fd 3 3< /path/to/a/secret/file \
< infile > outfile
This is a more advanced method to give the passphrase, it is
equivalent to Option -p of gpgwrap. This example should at
least work with the bash.
11.
gpg --batch --no-tty --passphrase-fd 3 \
3< <(echo "mysecretpassphrase") \
< infile > outfile
Like above, but the passphrase is given directly. This example
should at least work with the bash.
BUGS
In version 0.02 of gpgwrap the exit code of gpg was only returned if
gpgwrap read the passphrase from a file. Since version 0.03, only -F
omits exit code checking by default, but it can be enabled with -c.
SEE ALSO
gpg, gpg-agent
AUTHOR
Karsten Scheibler
gpgwrap 0.04 gpgwrap(1)